Automatic engine synchronizer



June 26, 1951 H. J. NICHOLS AUTOMATIC ENGINE sYNcHRoNIzER 2 Sheets-Sheetl Original Filed June 6, 1941 o Sme/MM' J /l//cHo/ s Gum/MMF,

June 26, 1951 H. J. NICHOLS 2,557,991

AUTOMATIC ENGINE SYNCHRONIZER Original Filed June 6, 1941 2 Sheets-Sheet2 Patented June 26,1951

Original applicationv `lune 6,-, 19,41, Serial No, 396,936, now PatentNo. 2,423,400, dated July Dividedand this application December 16',1944,;Serial No. 568,497

16 Claims.. (Cl. 17o-135.29)

This invention relates to automaticsynchro# nizing systems for engines.More particularly it relates to automatic synchronizing systems forcontrol-ling the relative rotations of a pluralityv oiengines, such asthe propeller driving` engines oi? aI multi-engine airplane, so as toestablish and maintain the revolutions of said engines in isochronousrotation and in substantially constantl phase relation, thatA is to say,so that the engines rotate not only at thesame speed, but also inpredetermined rotational relation with respect to an invariable part oftheir respective cycles oi rotation'.

Engines so rotating are said to be running in unison.

This application is a division of my applica-i tion Serial No. 396,936,led. June 6, 1941', Which issued as U. S. Letters Patent No. 2,423,400,dated July l, 1947. 'lt is Well known that inthe operation oi? ine.stallations of multi-engines intended to run att-he saine speed, anyvariation in the speed of the' individual engines produces undesirableand y harmful vibrations. It is also known that'. wheny ordinary speedfregulating Igovernors are utilized to control the speed of" theindividual engines of a multieengine installation, even when thegovernors of the individual engines are mostcareiully adjusted'to thesame'speed' setting, pro.- nounced rhythms and minor variations in theengine speeds may occur, producing undesired beats and vibrations.Moreover, large periodically moving parts of adjacent engines-such aspistons and connecting rods, may produce 11n- Wanted resonant effectswhen the engines are running at the same speed, unlessY measures aretaken to keep the engines out oi step. Hence, s uchY installationsrequire constant attendance and monitoring by an operator to keep theengines running in smooth. relation. This situa: tion appliesparticularly to multi-engine airplanes having controllable pitchpropellers under governor control, hence the present invention will bedescribed and illustrated with particular refer-4 ence to. suchapplication. It is to be understood, however, that the invention isgenerally applicable-to, the synchronizationof a plurality of' enginesor prime movers to obtain smooth running.

A principal object of the invention is to provide automaticsynchronizing apparatus especially adapted for use in connection withcentrifE ugal'speed regulating governors for the individual enginesoi amulti-engine installation, thereby to establish and maintain unison ofthe several en gines.

A` further object of the invention is to. provide means whereby aplurality of propellers,' driven by individual engines,` can b esynchronized :irriter-l m'atically. That is they can be established andmaintained' in' rotation isochronousl-y and substanti'allyl in *constantphase relation v v-'itlfiout monitoring by an'operator. According tothe'i-ni' vention, for purposes of'vsuch synchronizatioI-r,I any one oftheplurality' of propeller engines-can be selectedr to function as theApace setter or leader, while the other engines are caused by theirself-synchronizing@ governorto function as followers orsl'a.f\es-,rtl1eirl speeds being vcorrected individually to keep them insynchron-ism with' the selected leader. Y Y y A further object isl tosupplementv the usual speed-regulating governor with auxiliary phase--Ycorrecting means whereby synchron-ism or a plu"-A ral-ity or engines canbef accurately and automatic-ally maintained indefinitely.

A fur-ther object is to provide synchronizing controlI apparatus whichis responsive to a change in rotar-y speed,l or relative phase, or both;

A further object is to provide-` auxiliary phase regulating means' foruse in conjunctionv with speed regulating governors. thereby to perfectthe speed regulation for purposes of' automatic syntchronization.

In the drawings:

Fig. 1 is al schematic diagram of' a; typical multi',y engine systemdriving controllable pitch propel', 1ers and including: thesynchronizing features oi' the invention.

Figi 2 is an axial section of a typical speed governor provided with asynchro..valve embody-e ing part of the invention. Fig. 3 is a partaxial section of` the governor of Fig.4 2, butv taken at-.f right anglesthereto." on line 3&3 of Fig. 2..;

Fig. 4 is a part section on line l-Tllof Fig.'2..

Referring now to Fig. l, the simplied multii-z engine, hydraulic,Vpropeller pitchecontrol systernthere'schematically shown utilizes aItypical,

speedecontrol governor, and'typical pitch'econtrol mechanismsuch as thatshown in my U'. Lets. ters Patent,` No; 2,423,400, issued J'uly'l,lll'i'fand in addition special and'- novel` devicesy forming part of thepresent invention for purposes or automaticy synchronization, allparticularly adapted to multi-engine, constant"speedA con; trollable.lpitchrv propeller installations for aire craft. In such installationaapracticalprohleni' off operation is presentedY hy thef surge and re-isonant vibration eiectsv dueto'the"beatll effect of powerful enginesrunning @approximately cr exactly the Same Speech but net in true unisonIt is known that the objectionable beat effects can be eliminated byproper synchronous operation of all engines, and that is the purpose ofthe embodiment now to be described.

The iirst of the special synchronizing devices is a pulsator device forproducing timed fluid control pulses indicative of the speed of rotationand a certain rotational position or phase of a master rotary element.In Fig. l, the pulsator device is shown for illustrative purposes ascomprising a cam-actuated circuit closer 90 driven by an associatedrotary engine or device controlling a solenoid-actuated, plunger valve85 which, in conjunction with pump 80, periodically produces a discreterluid impulse indicative of the speed and phase of the master rotaryelement, be it a rotary element of the engine, the propeller, or amaster speed device functioning as the pace setter. In the case showncam Si can be considered as being driven by its associated engine whenthat engine has been selected to function as leader.

However, in adapting the invention to typical control systems, thepulsator apparatus can have other forms so long as it is capable ofproducing timed fluid impulses of the control medium indicative of theperiodicity and phase of the master rotary element of the synchronizingsystem. For example, the periodic current impulses produced by circuitcloser 9B could serve as the phase indicator of the crank shaft of theengine by which it is driven, or of a propeller which the engine drivesthrough reduction gearing or of an independent master timing deviceproducing impulses of proper speed. Likewise, the pulsator means couldcomprise a rotary valve adapted to produce a pulse for each revolution.

, The small accumulator cylinder 83, while not an essential part of thepulsator system, aids in producing discrete iiuid impulses moreecientlyl Between impulses, the pump 80 charges the accumulator cylinderagainst the spring-loaded piston 84 therein. The second of the specialdevices is a phasing device, herein termed the synchro-valve 15, whichautomatically compares the phase, that is to say the relative angularposition, of a follower rotary element with the master rotary element inthe synchronizing system, and also produces corrective eiTects toestablish and maintain unison. Here again, alternative or equivalentforms of the phasing device, such as a cam driven selector valve, can beutilized in some cases in adapting the invention to typical controlsystems. `By means of the phase comparing and phase correcting devicesof the invention in conjunction with the pitch-changing mechanism andcontrol elements already described (or equivalent apparatus) theautomatic synchronization of a plurality of propellers or engines can beeifected. Turning now to Fig. 1 in detail, the electrical circuit closer90, of any suitable construction, as for example a cam-operatedcontactor as shown, is assumed to be driven at the leader speed,although in practical operation it may be driven at half speed, or atsome other appropriate proportional speed. During a fraction of arevolution of the cam 9|, say 1/3 revolution, the circuit closercontacts close and supply a pulse of electrica1 current to energize thesolenoid 94. In response to the energization of the solenoid 94, theplunger 86 momentarily opens the duct 81, so that fluid under pressureis deliveredby accumulator 83 in the form of a pulse via the connectingconduit to the inlet port 1l of the governor selector valve 10.

The uid supplied by pump is assumed to be under suicient pressure sothat when fluid pulses are applied to the pitch control mechanism,substantial pitch control action will ensue. But at other stages of thecontrol cycle, the iiuid pressure beyond the valve 85, due to leakage orbleeding, remains below the effective control level.

V'lhus while limited uid pressure may be applied by the governor |00 orthe synchro-valve 15 to the pitch control mechanism at any time, the uidpressure is only effective for control action during the pulse stage,and therefore the fluid pulses effectively represent for controlpurposes the speed and a predetermined phase of the leader by which thepulsator is driven.

The synchro-valve 15, which may be located in the hydraulic systembetween the governor Valve 10 and the pitch control mechanism as shownbut in any case in series with the pulsator valve, has an inlet port 1lconnected to the inlet port 1i of the governor, and hence to thepulsator valve, and has outlet ports 11-18 connected to the hydraulicfluid conduits F and C leading to the pitch control mechanism asindicated. Synchro-valve 15 also has a rotary valve element, shown as arotary synchro vane 19, driven by and in proper ratio to the speed ofits associated engine, which engine also drives the associated governor1D0. Hence one end or the other of the vane can be caused to cover theinlet port 1 l substantially during each pulse arrival when itsassociated `driver is functioning as pace-setter.

This rotary synchro vane 19 is in a sense the functional inverse of thepulsator cam 9|, in that it represents the phase of its driver, but bycontrast it blocks the transmission of fluid during a fraction of arevolution comparable to the duration of the received control impulse,and permits transmission of fluid during substantially the remainder ofthe revolution. Furthermore, by its momentary angular position relativeto the arrival of the control pulses at the inlet port 1l the vane 19compares the phase of its driver with that of the pulsator driver. Thisfunction of comparing the phase of the follower with that of thepace-setter is as essential to the synchronizing system described as thefunction of comparing the speed of its driver with that of a standardspeed is to a speed governing system.

The synchronizing governor Referring to Fig. 2 generally, the governor|00 there shown has the combined functions of regulating the enginespeed and establishing and maintaining synohronism by control of thepropeller pitch as described hereinafter. The speed regulating functionis eXercized by ya, well-known type of speed-calibrated fly-weighthydraulic governor' which has been 4widely applied to the control ofconstant-speed controllable pitch propellers. The automaticsynchronizing function, however, is accomplished by special additionalfeatures and because of this unique additional function, the governor asa whole is termed a synchronizing governor. lIfhe principle andconstruction of {dy-weight governors being well known, extensivedescription here is deemed unnecessary. However, the novel featuresrelating particularly to the invention will be pointed out and fullydescribed. Referring now to Figs. 2-4 in detail, the governor `assemblycomprises; a r heart Ii't,v andy body .m2, the. latter' mounted with aipad: 128.10m; an engine casing 4B. Within the head and -body is arevolving fly-weight mechanism` lub driven` by the neck '99', which.inturn is driven by the engine at a desired speedratioproportionaltotheengine speed in thel usual manner.. The neckA`Elli is provided with ports 'i it', 1:2, and lf3; and' enclosesslidable valve-plunger lil; Theily-weight mechanism includes two pivotedcentrifugal bell-cranks or ily-balls?" ills operating against. aSpeederspring i011?, the latterb'eing' adjustablv tensioned by.' rackw51 andf pinion it@ to set the desired engine speed. Stops im andl H18;secured on plunger 10, limit' the speed range'` and. enable the plungerto be moved arbitrarily up or down by the cock-pit controls, butprovide-a working range therebetween. In Figs. Z and 3`the plunger '10Cis shown in the mid neutralposition;F 1 y The neck Sli'A is alsoprovided with a; gear m9 'which drives a mating' gear' ii tol form yauidpump Si), in well known manner, The pump 80 is provided with a springloaded pressure-relief valve 8i. Thisreliefl valve can be equipped, ac-`cording to commonpractiee, for'quick' increase of the spring pressurefor propeller fa-thering.

The gear IBS also meshes with a gear lll which rotates the synchro-vaneT9 at'the proper predetermined speed ratio. The synchro-vane is'provided with two arcuate opposite grooves 16 (one being in View inFig. 2) connected vertically on opposite sidesY with ring ports H and'l'8- respectively, the actual arrangement being equivalent to thediagrammatic rotating vane T9? of Fig. l. Referring to Figs. 3 and 4 inconnection with Fig. 2, suitable ducts l2-l-I25 inpad i213, assembledbetween the engine 40 andthe governor body H32, connect the oill columnof the suction duct Mt (leading from` the oil supply pumpto the governorboss) to valve 8 I, Iand thence'to the annular duct 52d. Thence-the-oildescends by duct i275 (see Fig. 3) te radial duct |526 toconnect withthe accumulator 83', andthe pulsator'valve: (indicated by plunger 86)which normally sev-ers the oil column at that point. Other minorducts-connect the ports of thev neck BStothe-pulsator valve 8E and tothe synchro-valve (see Fig. 2).

Briefly, the operation ofthe governor in connection with speedregulation is as follows: The switch X is moved tothe S or startposition and the cock-pit controls are manipulated bythe pilot oroperator tomove therack |05 to adjust the compression force onSpeeder-spring lillk to the calibrated speed level. The governorthereupon slides plunger 'It up ord'owh, `according' to whether they-weig'htsmove radially outor in at the existing speed, and therebyregulates the propeller pitch changing mechanism'tofenable the engine torun atthe desired-l speed. Atsubstantially calibrated speed, thefly-weight force'and the spring force balance, bringing the plunger 'l-Uto rest in the neutral' position as shown in- Figs. 2 and 3. The leaderengine isthenfselected'by the operator by means of switch X (Fig-gl),whereupon the solenoid. pulsator valves are'p'eriodically energized'bythe operative circuit closer Sol driven by the. selected leader engineas previously described.. The pulsatorv plunger Bti admits pulseg offluid.V to'v the: inlet ,port 'H ofA neck 99, andtoV the inlet port 'lilof. thesynchro-valve. Depending on thephase.` relation ofwane 1:9 withreference to the'inletportz'li' at thef'instant of arrival of successivepulses, asfdescribe'd in connection 'with synchronization. thepitbh-changing mechanism is further regulated byv vane lsf inmicrometric degree to establish andmaintain synchronism of the followerengine -withthe leader engine. Naturally,l if the propellers. are drivenat engine speed, or ata, -xed ratio thereto as usually practiced, the:propellers are likewise automatically maintained in synchronism.

Automatic synchronization The operation of the automatic synchronizingsystem is as follows; Let engine A,. assumed to be driving cam 9i,represent the master element, and engine B the follower element. Thepreliminary operation ofI bringing both the master and follower enginesto the desired approximate or parity speed is accomplished by theoperator who by reference to calibrated'V speed indicating instruments,as for example engine tachometers, sets the respective enginel throttlesand governor controls at the proper settings. whereupon-,- the enginesdeliver the requisite power andthe governors automatically adjust thepitch of the respective propellers to obtain constant speed under theexisting operating conditions as previously described. (During thisperiod ofestablishing speed parity, the solenoidpulsator valves can bekept open by throwing the pulsator switch X to the S" or start-position,thereby increasing the governor action. On reaching speed parity', theswitch X should bemoved either to the a or b position, thereby toselectone engine or the other to act as leader.)v

Assuming now that the circuit closer cam 9|- is driven by engine A(which cam indirectly actuates the pulsatorsof both engines as indicatedin Fig. l) and thatr the low point of this cam represents the masterreference phase, while the synchro-vane 159 of engine B represents thefollower phase, it is evident that as the engine speeds approach but donot attain exact parity there will be a gradual relative precession inphase between these elementsone way or the other. Let it be supposedthat engine B is the faster. Hence, after reaching the speed where the Bsynchro-vane 19 covers the inlet port H during the pulse interval, the Bsynchrovane 19 will thereafter advance or lead in phase relative to thearrival of ther impulse at the inlet port. As it does so, the inlet portil becomes uncovered during the pulse interval, as indicated for engineB in Figi 1, and the pulses will be admitted by the B synchro-vane tothe inlet 78, leading to the C conduit, without any necessity ofspeed-governor action. The resulting coarsening of the pitch will tendtoslowA down the-follower engine, hence eventually the speed ofi thefollower will be below parityand thesynchro-vane will beginY toretrogress; It willoontinue todo so until the inlet port H isV againcovered during the pulse interval, and thereafter the synchro-vane willlag inl phase with respect to the pulses. 'lhereupon'thel pulses will beadmitted to port l1 and the F conduit toiine the pitch. As before,`thiscorrective action is accomplished-,solely by the agency of the synchro:-valve, without governor action. Assuming' that the synchro-vaneovershoots and commences to lead on the next excursion,v the speeds willbe nea-rer parity' and the corrective action will" be less; Thus, like-aheavily'damped pendulum, the synchro-Vane will quickly bring itsassociated follower engine into stepat the meanof its swings, whereatthe.' port ll' isV closed by the synchro-vane 'i9 in coincidence withvthe pulse arrival, as-ior engine A`in theriigure: Thisf's .thestablecondition of unison or perfect syn- .chronism.

Synchronism having been automatically established as just described, thesynchro-valve of the follower engine thereafter functions as amicrometric speed adjuster by correcting the phase of the followerengine responsively to any change of relative phase, so as to maintainsynchronism, and the governor is relieved of any speed adjustingfunction during minor speed variations. But with respect to major speedadjustments due to varying loads, etc., the governor functions in normalmanner to maintain constant speed. Final parity of speed and truesynchronism of each follower engine are thus automatically establishedand maintained by its individual synchro-valve.

p Hence, in eifectthe synchronizing additions provide not only aform ofmicrometric speed adjustment, but also automatically correct the phaseof the follower to perfect the synchronization so as to obtainsubstantial unison. This is believed to be a novel and highlyadvantageous feature for precision governors, applicable generally tothe governing and automatic synchronization of engines of various types.

It will be apparent to those skilled in the art that the principles andconstructions of the twoengine automatic synchronizing system asdescribed can be extended to multi-engine installations generally merelyby duplication of minor additions of conventional apparatus such asswitches, etc.

Without further explanation or discussion, it is believed that theforegoing conveys a good understanding of the manifold novel featuresand advantages characterizing the invention. These features andadvantages cooperate harmoniously with the essential considerations inspeed governors to provide a light weight, reliable, compact, efficientinexpensive and relatively simple automatic synchronizer.

Without further analysis the foregoing will so fully reveal the gist ofthis invention that others can by applying current knowledge readilyadapt it for various applications without omitting certain featuresthat, from the standpoint of the prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention andtherefore such adaptations should and are intended to be comprehendedwithin the meaning and range of equivalency of the following claims.

I claim:

,1. In automatic synchronizing apparatus for a system of mechanicallyindependent rotary power drivers, in combination, centrifugal speedgoverning means for regulating the rotary speed of each of said drivers,means for producing periodic hydraulic impulses each indicative of thecompletion of a certain cycle of 4rotary motion of a selected one ofsaid drivers, and means for automatically utilizing said impulses toestablish and maintain synchronism of the other of said drivers withrespect to said selected driver.

2. In governor apparatus for synchronizing a system of rotary mechanicalpower drivers, speedcontrol means, including centrifugally actuatedmechanism, for governing the rotary speed of each of said drivers,pulsator means including a rotary element driven by one of said driversfor producing timed hydraulic impulses indicative of the speed and phaseof its associated driver, and means including a rotary element driven bya second driver for utilizing said impulses to adjust the speed of saidsecond driver to rotate in unison with the first named driver.

3. In synchronizing control apparatus for a rotary mechanical powerdriver, in combination,

' centrifugal speed regulating means for said driver, rotary phasecorrecting means for said driver, and hydraulic controlled means forvarying the load torque responsively to the joint control of said speedregulating means and said phase correcting means.

4. In synchronizing control apparatus for controlling the speed of aplurality of engines, in combination, a centrifugal speed regulatinggovernor for each engine, means for generating impulses indicative ofthe speed and phase of one of the engines, and means operativelyassociated individually with each of the other engines for utilizingsaid impulses to regulate the speed and phase of its associated engine,thereby to cause all of said engines to rotate in unison.

5. In a self-synchronizing speed governor, the combination of acentrifugal speed-responsive device, a hydraulic regulating valveactuated by said device, an auxiliary rotary hydraulic regulating valve,and means for rotating said device and said rotary valve in xed rotaryrelation.

6. In a system of controllable pitch propellers, a drive engine forrotating each propeller, pitchcontrol means operatively associated witheach propeller, and hydraulic synchronizing means for causing the saidpropellers to rotate in unison by controlling the pitch thereofincluding speedgovernor means for each pitch control means, meansincluding a pulsator for producing timed hydraulic pulses, and meansresponsive to said hydraulic pulses for automatically regulating thepitch control means as required to establish and maintain unison ofrotation of said propellers.

7. In driving and synchronizing means for a plurality of controllablepitch propellers, a driver motor for rotating each propeller, pitchcontrol means operatively associated with each propeller, and means forsynchronizing said propellers including adjustable means for governingthe speed of each motor under varying operating conditions thereby toestablish substantial speed parity of the propellers, means forgenerating timed hydraulic pulses indicative of the phase of oneselected propeller, and hydraulic means for comparing the phase ofothers of the propellers with the phase of the one selected propellerand regulating the pitch control means as required to establish andmaintain unison of rotation of the several propellers.

8. In synchronizing means for a plurality of motors independentlydriving controllable pitch propellers, individual means for governingthe speed of the motors, and means automatically operative to establishand maintain synchronism of said plurality of motors, including impulsegenerating means for producing timed impulses indicative of the phase ofa selected leader motor, and means for utilizing said impulses tocompare the phase of a follower motor with the leader motor andaccordingly regulating the phase of said follower motor so as to bringsaid follower motor into unison with said leader motor.

9. In synchronizing speed-control means for controllable pitchpropellers, in combination, individual speed-governing means for eachpropeller, and automatic synchronizing means for at least one of saidpropellers, including means for generating periodic hydraulic impulseseach indicative of the phase of a rotary controlling element, andhydraulic means for comparing the phase of a rotary controlled elementwith that of said controlling element and for regulating accordingly thepitch of a controlled propeller so as to establish and maintain unisonof rotation with the said controlling element.

10. In a system of controllable pitch propellers, in combination,driving means for rotating each propeller independently, means foradjusting the pitch of each propeller; and speed-governor means forcausing said driving means to rotate in unison, including an adjustableconstant-speed control device for each driving means, means forgenerating periodic hydraulic impulses, and automatic synchronizingmeans for utilizing said periodic hydraulic impulses to actuate saidpitch adjusting means jointly with said constant-speed control device,thereby to establish and maintain unison of rotation between the saiddriving means.

11. In a synchronizing system for a plurality of controllable pitchpropellers, in combination, drive means for rotating each of saidpropellers independently, individual constant-speedy governor means forregulating the speed of each said drive means by Varying the pitch ofits associated propeller, a rotary leader element motionally ooordinatedwith an individual drive means, means operatively associated with saidleader element for producing periodic hydraulic impulses indicative ofthe speed and phase of said individual drive means, a phase-comparingrotary device motionally coordinated with another propeller drive means,and means for utilizing said periodic impulses to synchronize saidrotary device with said leader element.

12. In an automatic synchronizing system for engines, the combination ofmeans for regulating the speed of an engine, and hydraulic means forminga part of said system and motionally coordinated with the rotation ofsaid engine for comparing the speed of rotation and phase of said enginewith respect to timed hydraulic control impulses produced by apace-setter.

13. In an automatic synchronizing system for engines, the combination ofgovernor means for y regulating the speed of each engine, a rotarypace-setter, means for producing timed hydraulic control impulsesindicative of the rotations of said pace-setter, hydraulic means forcomparing the speed and phase of a follower engine ,I

14. A synchronizing control system for synchronizing the rotations of asystem of rotary units including, in combination, speed regulatingmeans, including a governor, for each rotary unit; means for selectingone of said units to act as a master unit; means for producing timedhydraulic impulses indicative of the speed and phase of said selectedmaster unit; and auxiliary speed control means operatively associatedwith each of said other units for utilizing said impulses to regulatethe rotations of its associated unit jointly with the governor of thatunit so as to cause said unit to rotate in unison with said selectedmaster unit.

15. In an automatic synchronizing control for synchronizing therotations of a power unit with those of a master unit, the combinationof a centrifugally actuated governor for controlling a speed regulatinghydraulic valve, and a rotary phase regulating hydraulic valveoperatively associated with said governor for comparing the rotationalphase of said power unit with that of said master unit and actingjointly with said governor to synchronize the rotations of said powerunit with those of said master unit.

16. Control apparatus for synchronizing the rotations cf a followerrotary unit with those of a master rotary unit including, incombination, means operatively associated with said master unit forproducing hydraulic impulses indicating the rotations of said masterunit, and means operatively associated with said follower unit forutilizing said hydraulic impulses in synchronizing the rotations of saidunits.

HARRY J. NICHOLS.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,886,975 Protlich Nov. 8, 19322,153,470 McNeil Apr. 4, 1939 2,173,913 Morehouse Sept. 26, 19392,224,177 Algarsson Dec. 10, 1940 2,250,695 Algarsson July 29, 19412,254,970 MacNeil Sept. 2, 1941 2,296,177 Newton Sept. 15, 19422,319,218 Drake May 18, 1943 2,330,070 Martin et al Sept. 21, 19432,340,994 Smith Feb. 8, 1944 2,374,276 French Apr. 24, 1945

